This will depend on each of country's tax laws if they explicitly or impliedly view cryptocurrencies as matters subject to be taxed. From what I know, some countries have started implementing laws, specifically on the tax aspect, with regards to cryptocurrencies in their country. But as far as those who illegalize and prohibit the utlization of such, then no laws are mentioned with regards to taxing (although they are prohibited).
Bitcoin is not designed for taxes to be paid on it. I beleive the best for government maybe to tax bitcoin users and make it more popular. Just that the charges should be considerate and proportional to the excesses.
Regarding the potential for tax revenues from digital currency transactions, such as bitcoins that are increasingly widespread but the article, bitcoin is not a legitimate means of payment So people do not use it as a payment system.
In fact, there are other services accepting bitcoin as an alternative payment for their services/products depending on the country. My wallet accepts transactions and payments for utility expenses and they are even connected to our various banks for online transfer of payment. This will heavily depend on the country if they allow such currency to be utilized or not.